Electronic systems and circuits have made a significant contribution towards the advancement of modern society and are utilized in a number of applications to achieve advantageous results. Numerous electronic technologies such as digital computers, calculators, audio devices, video equipment, and telephone systems have facilitated increased productivity and reduced costs in analyzing and communicating data, ideas and trends in most areas of business, science, education and entertainment. Frequently, these advantageous results are realized through the use of information stored on memory media and manipulated by a processing device. The configuration and type of memory utilized to store the information can have significant impacts on information processing performance.
Numerous electronic devices include processors that operate by executing programs comprising a series of instructions for manipulating data in the performance of useful tasks. The programs and associated data are typically stored in a memory location with a unique indicator or address. The utility a processing device provides often depends upon the amount of information a memory stores and the speed at which it is accessible. The ability to access a memory and transfer information quickly and conveniently usually has a significant impact on information processing latency.
Magnetic memories are a type of memory that usually offer many advantages. For example, magnetic memories perform read and write operations much faster and consume less power than other types of short term and long term memory, such as dynamic random access memories (DRAM), synchronous random access memory (SRAM), flash memory and traditional hard drives. Magnetic memories can also typically perform read and write operations much faster (by orders of magnitude) than conventional long-term storage devices such as hard drives. In addition, magnetic memories are typically more compact and facilitate the storage of more information in a smaller space than other types of traditional memories.
A typical MRAM device includes an array of memory cells with word lines extending along rows of the memory cells and bit lines extending along columns of the memory cells. Each memory cell is located at a cross point of a word line and a bit line. The memory cells are usually based on tunneling magneto-resistive (TMR) devices such as spin dependent tunneling (SDT) junctions. A traditional SDT junction includes a pinned layer, a sense layer and an insulating tunnel barrier sandwiched between the pinned and sense layers. The pinned layer has a magnetization orientation that is fixed so as not to rotate in the presence of an applied magnetic field strength within a defined range. The sense layer has a magnetization that can be oriented in either of two directions, the same direction as the pinned layer magnetization or the opposite direction of the pinned layer magnetization.
The magnetization orientation of the pinned layer is fixed, typically by an underlying antiferromagnetic (AF) pinning layer. The pinned layer in some traditional magneto-resistive memory devices may have a net magnetic moment, which leads to undesirable effects. One such effect is that of a demagnetizing field. For example, a magnetic field from the pinned layer reaches and interacts with the sense layer in a manner that leads to loss of data if this magnetic field becomes too strong. In addition, the presence of the magnetic field from the pinned layer usually leads to the requirement that an asymmetric magnetic field be used to switch the state of the data layer, which typically adds to the complexity of the writing process. Further complications also often arise since the tolerance for stray magnetic fields during writing is lowered.